I was doing something with a PR9 recently and IIRC, the pilot seat is an MB Mk.3 and the navigators seat a Mk.4 - both very pretty ergonomic nightmares, although obviously there's an element of tweaking quite often to a model to fit the aeroplane. I suspect that you are therefore dealing with two Mk.3s ?
Martin Baker still maintain good data on just about everything they ever did, so you might get some drawings and specifications out of them?
The other place to ask would be the Yorkshire Air Museum at Elvington:
English Electric Canberra T4 they're people with a good reputation for preserving historical data and might, for example, have some maintenance manuals?
G